I upgraded just now (upgraded: 5.7.3_20 -> 5.8) and it fails to start. mibII/mta_sendmail.c:open_sendmailst: could not guess version of statistics file "/var/log/sendmail.st" - & 'Error opening specified endpoint "udp:10.55.0.39:161"'I went so far as to follow "the recipe" again: https://dan.langille.org/2015/09/07/installing-net-mgmtnet-snmpd-a…

config

[dan@dev-nginx01:~] $ grep snmp /etc/rc.conf
snmpd_flags="-a -r"
snmpd_conffile="/usr/local/etc/snmpd.conf"
snmpd_enable="YES"

diff

[dan@dev-nginx01:~] $ diff -ruN /usr/local/share/snmp/snmpd.conf.example /usr/local/etc/snmpd.conf
--- /usr/local/share/snmp/snmpd.conf.example	2019-09-30 13:09:19.788339000 +0000
+++ /usr/local/etc/snmpd.conf	2019-09-30 12:29:05.687513000 +0000
@@ -12,7 +12,7 @@
 #
 
 #  Listen for connections from the local system only
-agentAddress  udp:127.0.0.1:161
+agentAddress  udp:10.55.0.39:161
 #  Listen for connections on all interfaces (both IPv4 *and* IPv6)
 #agentAddress udp:161,udp6:[::1]:161
 
@@ -74,8 +74,8 @@
 
 #  Note that setting these values here, results in the corresponding MIB objects being 'read-only'
 #  See snmpd.conf(5) for more details
-sysLocation    Sitting on the Dock of the Bay
-sysContact     Me <me@example.org>
+sysLocation    BSD Cabal HQ
+sysContact     dan@langille.org
                                                  # Application + End-to-End layers
 sysServices    72
 
@@ -191,3 +191,6 @@
                                            #  Listen for network connections (from localhost)
                                            #    rather than the default named socket /var/agentx/master
 #agentXSocket    tcp:localhost:705
+
+extend nginx            /usr/local/etc/snmp/nginx-stats
+extend phpfpmsp         /usr/local/etc/snmp/phpfpm-sp
[dan@dev-nginx01:~] $ 

error

[dan@dev-nginx01:~] $ tail /var/log/snmpd.log
mibII/mta_sendmail.c:open_sendmailst: could not guess version of statistics file "/var/log/sendmail.st"
Turning on AgentX master support.
Error opening specified endpoint "udp:10.55.0.39:161"
Server Exiting with code 1
[dan@dev-nginx01:~] $ 

ifconfig -a

[dan@dev-nginx01:~] $ ifconfig -a
ix0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=e53fbb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,LRO,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
	ether 00:25:90:fa:0f:10
	media: Ethernet autoselect
	status: no carrier
ix1: flags=8802<BROADCAST,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=e53fbb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,LRO,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
	ether 00:25:90:fa:0f:11
	media: Ethernet autoselect
	status: no carrier
ix2: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=e53fbb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,LRO,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
	ether 00:1b:21:39:a9:c5
	inet 10.55.0.39 netmask 0xffffffff broadcast 10.55.0.39 
	media: Ethernet autoselect (10Gbase-SR <full-duplex,rxpause,txpause>)
	status: active
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
	options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
	groups: lo 
pflog0: flags=141<UP,RUNNING,PROMISC> metric 0 mtu 33160
	groups: pflog 
[dan@dev-nginx01:~] $ 

pkg info

[dan@dev-nginx01:~] $ pkg info net-snmp
net-snmp-5.8
Name           : net-snmp
Version        : 5.8
Installed on   : Mon Sep 30 15:50:18 2019 UTC
Origin         : net-mgmt/net-snmp
Architecture   : FreeBSD:12:amd64
Prefix         : /usr/local
Categories     : net-mgmt ipv6
Licenses       : BSD3CLAUSE
Maintainer     : zi@FreeBSD.org
WWW            : http://net-snmp.sourceforge.net/
Comment        : Extendable SNMP implementation
Options        :
	AX_DISABLE_TRAP: off
	AX_SOCKONLY    : off
	DOCS           : on
	DUMMY          : on
	JAIL           : on
	MFD_REWRITES   : off
	MYSQL          : off
	NEWSYSLOG      : on
	PERL           : on
	PERL_EMBEDDED  : on
	PYTHON         : off
	SMUX           : off
	TKMIB          : off
	TLS            : off
	UNPRIVILEGED   : off
Shared Libs required:
	libpkg.so.4
	libperl.so.5.30
	libpcre.so.1
Shared Libs provided:
	libnetsnmpmibs.so.35
	libnetsnmp.so.35
	libnetsnmphelpers.so.35
	libnetsnmpagent.so.35
	libnetsnmptrapd.so.35
Annotations    :
	FreeBSD_version: 1200086
	cpe            : cpe:2.3:a:net-snmp:snmp:5.8:::::freebsd12:x64
	repo_type      : binary
	repository     : local
Flat size      : 12.2MiB
Description    :
This is Net-SNMP (previously known as "ucd-snmp").

Various tools relating to the Simple Network Management Protocol including:

    An extensible agent
    An SNMP library
    tools to request or set information from SNMP agents
    tools to generate and handle SNMP traps
    a version of the Unix 'netstat' command using SNMP
    a graphical Perl/Tk/SNMP based mib browser

WWW: http://net-snmp.sourceforge.net/
[dan@dev-nginx01:~] $ 

root@jfbsd12:/usr/local/etc # ifconfig lo1
lo1: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
        options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
        inet 172.31.5.12 netmask 0xffffffff
        groups: lo

root@jfbsd12:/usr/local/etc # netstat -anf inet | grep 161
udp4       0      0 172.31.5.12.161        *.*

root@jfbsd12:/usr/local/etc # ps ax | grep snmp
97935  -  SJ   0:00.02 /usr/local/sbin/snmpd -p /var/run/net_snmpd.pid

root@jfbsd12:/usr/local/etc # diff -u /usr/local/share/snmp/snmpd.conf.example snmpd.conf
--- /usr/local/share/snmp/snmpd.conf.example    2019-09-30 13:55:40.640371000 +0000
+++ snmpd.conf  2019-09-30 13:59:17.761955000 +0000
@@ -12,7 +12,7 @@
 #

 #  Listen for connections from the local system only
-agentAddress  udp:127.0.0.1:161
+agentAddress  udp:172.31.5.12:161
 #  Listen for connections on all interfaces (both IPv4 *and* IPv6)
 #agentAddress udp:161,udp6:[::1]:161

Tested with generic snmpd.conf, changed

agentAddress udp:127.0.0.1:161

to

agentAddress udp:193.105.105.132:161

Result: snmpd starts.

So something with lo0 ?

In my case, this is a jail without lo0 having 127.0.0.1

This worked before. No configuration file changes.

if I comment out this in /etc/rc.conf:

#snmpd_conffile="/usr/local/etc/snmpd.conf"

It runs:

[dan@dev-nginx01:~] $ sockstat -l | grep 161
root     snmpd      72144 6  udp4   10.55.0.39:161        *:*
[dan@dev-nginx01:~] $ 

tested with 127.0.0.2 as alias on lo0, works.

Tested with 127.0.0.1, does not work. Interesting.

Interesting.

[dan@dev-nginx01:~] $ sudo service snmpd restart
snmpd not running? (check /var/run/net_snmpd.pid).
Starting snmpd.
[dan@dev-nginx01:~] $ ': sockstat -l | grep 161
root     snmpd      66557 8  udp4   127.0.10.1:161        *:*
root     snmpd      66557 9  udp4   10.55.0.39:161        *:*
[dan@dev-nginx01:~] $ ps auwwx | grep snmp
root       66557  1.5  0.0  29700 16612  -  SJ   16:56   0:00.01 /usr/local/sbin/snmpd -p /var/run/net_snmpd.pid -c /usr/local/etc/snmpd.conf -a -r
dan        67550  0.0  0.0  11292  2612  0  S+J  16:57   0:00.00 grep snmp
[dan@dev-nginx01:~] $ grep Address /usr/local/etc/snmpd.conf
agentAddress  udp:127.0.10.1:161
#agentAddress  udp:10.55.0.39:161
#agentAddress udp:161,udp6:[::1]:161
                                                 #     and check the 'agentAddress' setting above
[dan@dev-nginx01:~] $ 

I added lo1 at 127.0.10.1

So why does this start now and listen on 10.55.0.39?

It's because for whatever reason, if you give it udp:127.0.0.1:161, it tries to open this twice and fails/aborts.

If you give udp:127.0.0.1:162, it opens both :161 and :162